An example of such a connecting structure is a structure where a valve which is an example of a fluid device is connected and coupled to an integration panel in which a fluid passage is internally formed, by causing a pair of supply/discharge flow paths to communicate with each other. Connecting structures are disclosed in Patent Reference 1 and Patent Reference 2. The connecting structure disclosed in Patent Reference 1 is a structure where a pair of supply and discharge flow paths are juxtaposed each other, and liquid-tightly connected and coupled to each other by plural bolts via annular gaskets which are independent of each other. The connecting structure disclosed in Patent Reference 2 is a structure where a pair of supply and discharge flow paths are juxtaposed each other, and a single gasket having a pair of flow path holes corresponding to the pair of supply and discharge flow paths is connected and coupled by using a single external screw nut.
Both of the connecting structures disclosed in Patent References 1 and 2 employ a structure in which many fluid apparatuses are integrately attached to a fluid block, or a so-called integrated piping structure. This is useful for compactifying or modularizing the whole of a piping system.    Patent Reference 1: Japanese Patent Application Laying-Open No. 2001-82609    Patent Reference 2: Japanese Patent Application Laying-Open No. 10-169859